A technique for reducing the switching loss by improving reverse recovery characteristics of a PN diode has been developed. Japanese Patent Application Laid-Open No. 2003-163357 discloses an MPS diode where a PIN diode is combined with a Schottky barrier diode. In the technique disclosed in Japanese Patent Application Laid-Open No. 2003-163357, injection of holes into an n− drift region from a p anode region is suppressed by reducing the size of the p anode region to a reach-through limit, and thus the switching loss is reduced. Japanese Patent Application Laid-Open No. 2000-323488 discloses a PIN diode provided with an n barrier region having an n type impurity with higher concentration than the concentration of an n− drift region between a p anode region and the n− drift region. In a technique disclosed in Japanese Patent Application Laid-Open No. 2000-323488, injection of holes into an n− drift region from a p anode region is suppressed by an n barrier region, and thus the switching loss is reduced.
Even in the technique disclosed in Japanese Patent Application Laid-Open No. 2003-163357 or Japanese Patent Application Laid-Open No. 2000-323488, despite only a few holes being injected into the n− drift region from the p anode region, the switching loss occurs. If injection of holes into the n− drift region is further suppressed, the switching loss of the diode may be further reduced.